The Kepler telescope has been searching in a tiny area of the galaxy for earth-sized planets – one quarter of 1 percent to be exact. During the past four years the telescope has already found 50 planets of that size.

Of course, these are just the earth-sized planets. NASA has a far bigger list of planets which could be habitable. There are 4,034 potentially habitable planets, 2, 335 of which have been confirmed as exoplanets after further observations.

Of the 50 earth-sized planets, 30 so far have been confirmed to exist withing the”Goldilocks zone” around their star (i.e. the planets are not too hot and not too cold to allow liquid water).

The Kepler telescope finds new planets by detecting the minuscule drop in a star’s brightness that occurs when a planet crosses in front of it.

However, NASA have been discovering more than just potentially habitable planets with Kepler. The search has allowed a research team to identify two distinct groups of small planets.

The team found a division between the sizes of rocky Earth-size planets and gaseous planets smaller than Neptune.

Most commonly, rocky planets were found to up to 75 per cent bigger than Earth, and about half of them seem to take on some hydrogen and helium, meaning their sizes swelled, allowing them to join the planets closer to the size of Neptune.

A graph showing the clear distinction in sizes between rocky planets. Source.

The clear distinction has allowed scientists to classify planets in a similar way to which biologists classify plants and animals.

Think, for example of the difference between a mammal and a reptile.

Of course, such information might eventually help narrow down the search for life “out there”. No news yet as to what alien life might look like – but hey we have movies for that right?